drivers/block/brd.c: fix brd_lookup_page() race

The index on the page must be set before it is inserted in the radix tree. Otherwise there is a small race which can occur during lookup where the page can be found with the incorrect index. This will trigger the BUG_ON() in brd_lookup_page(). Signed-off-by: Brian Behlendorf <[email protected]> Reported-by: Chris Wedgwood <[email protected]> Cc: Jens Axboe <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
mrcsosa · May 24, 2013 · dfd20b2 · dfd20b2
1 parent e5ee730
commit dfd20b2
Showing 1 changed file with 2 additions and 2 deletions.
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
@@ -117,13 +117,13 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
 
 	spin_lock(&brd->brd_lock);
 	idx = sector >> PAGE_SECTORS_SHIFT;
+	page->index = idx;
 	if (radix_tree_insert(&brd->brd_pages, idx, page)) {
 		__free_page(page);
 		page = radix_tree_lookup(&brd->brd_pages, idx);
 		BUG_ON(!page);
 		BUG_ON(page->index != idx);
-	} else
-		page->index = idx;
+	}
 	spin_unlock(&brd->brd_lock);
 
 	radix_tree_preload_end();